The present invention relates generally to abrasive belt sanding and polishing machines, and more particularly to means for controlling the positioning of an endless abrasive belt relative to the surface of a workpiece as the workpiece is transported by an infeed conveyor and into contact with an endless abrasive belt. More specifically, the present invention relates to means for controlling the configuration of the individual segments of a multi-segment platen so as to define or delineate the position, path and plane of the endless abrasive belt as it moves within the working station and forced into contact with the surface of the individual workpieces.
Certain varieties of wood, such as walnut, oak, birch and the like are desirable for use in the furniture industry, particularly because of their surface properties and pleasing appearance. However, because of their cost and decreasing availability, particularly as compared to the availability of more common woods or materials of construction such as fir, pine and particle-board, thin films or sheets of walnut or oak veneer are utilized, with the sheets of veneer being bonded or otherwise secured to the less expensive substrate or core. Either solid wood cores or cores made of particle-board material are widely employed and laminated panels with veneer surfaces are, of course, in widespread use in the furniture industry as well as in the construction industry.
In the furniture industry in particular, it has become commonplace to utilize veneer patterns of relatively non-abundant woods on a core or substrate of a relatively abundant wood. Sheets of veneer typically have a thickness of about 1/28th of an inch, and because of the techniques used in their preparation, veneers normally have an unfinished and/or rough surface texture. In the preparation of patterns of woods utilizing veneer surfaces, the individual pieces of veneer are selected and initially adhesively bonded to the surface of a core panel under pressure. In order to improve handling operations and to protect the exposed or outer surface of the veneer during the bonding operation, a paper surface layer or film is utilized. After completion of the bonding operation, the protective layer remains in place, and individual veneered panels are subjected to a sanding operation in order to remove the paper layer, remove surface irregularities and to prepare the veneer surface for later finishing operations. For the paper-removal operation, a cross-belt moving in a direction transverse to the direction of motion of the work is preferably utilized, while for finishing operations, a wide-belt moving along an axis parallel to the movement or motion of the work is normally utilized. Cross-belts have been found preferable for paper layer removal. In order to achieve and enhance operational efficiencies for these operations, a sanding and polishing machine may be provided with cross-belts and wide-belts arranged in tandem. As in the apparatus of the present invention, a sanding and polishing machine is provided with tandemly arranged cross-belts and longitudinally moving wide-belts.
In the treatment of individual workpieces, particularly veneered workpieces, the endless abrasive belt is typically backed with a resiliently biased pressure-pad. The resiliently biased pressure-pad is preferably in the form of a segmented platen, with the individual segments being provided with a pressure-bias so as to form a composite platen with a controlled profile of bias or advanced segments. For controlling the pad pressure across the surface of a workpiece, it has been found desirable to employ a platen comprised of a series of individually actuatable segments or portions. Such segmented platen means are known in the woodworking industry. Typically, preselected segments of the platen will be advanced outwardly, so that those preselected segments will be held or urged against the surface of the workpiece being treated. For many woodworking operations, it is desirable for the width of that portion of the platen which is to be held or urged against the workpiece be accurately controlled. In order to increase the degree or extent of control, the incremental size or width of each of the segments may be reduced. It has been found, however, that by merely reducing the size of the individual segments, the edge surfaces of certain types of individual workpieces being treated, including veneered workpieces, may be adversely affected due to dubbing, or other undesirable or anomalous edge treatment. The present invention reduces the problems of adverse edge treatment while preserving the desirable feature of reduced segment size. In particular, the utilization of individually actuated diaphragm cylinders has made it possible to contgrollably reduce the size of the individual platen segments, while maintaining accurate and positive control of the operation of each individual platen segment.
Typically, the advancing of individual platen segments, and the pressure exerted by each individually advanced platen segment against the surface of the workpiece is controlled by a workpiece sensor. The sensor is normally positioned along the infeed conveyor at a point up-stream from the working station in which the platen is disposed. This working station may employ either a cross-belt operating transversely to the axis of motion of the conveyor, or a wide-belt operating generally parallel to the axis of motion of the conveyor. In order to enhance the treatment of the surface of the workpiece, particularly as the workpiece is passing through a cross-belt working station, it is desirable that the operator be given the ability to widen the actual or operative width of that part of the platen which is advanced against the workpiece by increasing the number of individual platen segments advanced to include those which lie transversely outwardly of the actual workpiece. This increase, in effect, artificially simulates a workpiece of greater width passing through the working station. Because of the difference in direction of motion of the cross-belt with respect to the direction of travel of the conveyor, it has been found desirable in certain instances to artifically simulate the workpiece in a non-symmetrical fashion, such as by adding a greater number of segments to be advanced on the down-stream edge of the cross-belt/workpiece interface than on the leading belt/workpiece edge interface.